Method and means for producing compressional waves



Aug: 11, 1931. M. R. HUTCHISON 1,818,950

METHOD AND MEANS FOR PRODUCING COMPRESSIONAL WAVES Filed Jan.- 5, .1927 2 Sheets-Sheet l ATTORNEY Aug. 11, 1931. M. R. HUTCHISON I 1,818,960

METHOD AND MEANS FOR PRODUCING COMPBESSIONAL WAVES Filed Jan. 5, 1927' 2 Sheets-Sheet 2 3 INVENTOR e7 6 7% WW1,

ATTORNEY Patented Aug. 11, 1931 UNITED STATES PATENT GFFHCE MILLER REESE HUTCHISON, OF LLEWELLYN PARK, WEST ORANGE, NEW JERSEY, AS-

SIGNOR, BY MESNE ASSIGNMENTS, TO ACOUSTIC PRODUCTS COMPANY, OF NEW YORK, N. Y., A CORPORATION OF DELAWARE METHOD AND MEANS FOR PRODUCING COMPRESSIONAL WAVES Application filed January 5, 1927. Serial No. 159,135.

My invention relates to certain new and useful improvements in methods and apparatus for producing and reproducing sound, of which the following is a full, clear, and

exact specification.

' the form or character of the vibration. This form is produced by the presence, with the fundamental tone, of a plurality of overtones or partials, every harmonic overtone having a frequency corresponding to a multiple of its "fundamental. Character or quality of musical tones depends upon the varying proportions in which these tones and overtones are combined; and the faithfulness with which these tones and overtones are reproduced determines the fidelity of the reproduction of the original sound.

In sound reproducers, such as radio loud speakers, it is posslble to create a magnetic oscillation corresponding substantially with the original tonal value; but up to the present time no satisfactory means have been found for converting this oscillatlon into an accurately corresponding sound wave of proper volume. A sound reproducer includes a magnetic responsive means, a sound producer,

and a sound amplifying means, although two of these elements are frequently combined in a single instrument. Thus, we may have a sounding element; such as a cone, serving 3 both as a sound reproducer and amplifier; or

we may employ a diaphragm of magnetic material responsive to the magnetic wave and which, at the same time, acts as a sound producer. In the latter case, a separate amplitying means is employed.

I Unfortunately, none of these elements is capable of complete response to all of the vibrations involved in a complex sound, as each possesses inherent characteristics which tend to modify and distort the wave. For

instance, if a. cone of sufficient size to give sat-- isfactory volume is employed, its physical mass is so great that its response to vibrations of high frequency is relatively feeble. Again, a magnetic diaphragm has a natural period ofvibration (i. e., note) to which it most readily responds; and it also unduly accentuates certain overtones the frequencies of which are inharmonic to its fundamental.

So, in the use of amplifiers, still further complications arise. The most available form is that of a resonant air column; but a resonant chamber likewise possesses a fundamental and series of overtones to which it primarily responds and, when associated with a diaphragm, tends to accentuate these tones at the expense of all others. To prevent this distortion, it has frequently been found desirable to minimize or destroythe resonant capacity; and sometimes this has been accompli shed by operating the amplifier with so little energy that it does not come into resonance.

One feature of my invention recognizes the foregoing, and may briefly be described as follows: I provide, in a single instru ment, a series of diaphragms or sounding bodies, all operated from a common source and each tuned, or possessing a particular natural frequency to which it most readily responds. It is within the scope of this invention to provide one of these tuned diaphragms for each note of the audible musical scale and, when so utilized, the response of each diaphragm to its own fundamental is so much more vigorous than its response to any other note that a substantially faithful reproduction of that note is obtained. Such diaphragms, however, when used alone, possess the limitations above noted,that is, a tendency to unduly respond to inharmonic overtones and a suppression of the true har monies, This impairs the quality or value a of the tone being reproduced. It is essential,

therefore, to remove these defects and to improve or control the overtone response, so as phragm, exercises a controlling action thereon sutlicient substantially to coerce the diaphragn'i into vibrating in step with it. This is especially important in the case of harmonic overtone treouencies. So eiiective is this action that. in many cases, it will be found unnecessary to tune the diaphragm sharp y. as the resonator action very largely preponcerates, is capable of forcing the diaphragm to respond to the resonator fundamental and harmonic overtones, and relatively suppresses the inharmonic overtones which the diaphragm would otherwise tend to accentuate.

One feature of my invention, therefore. compri a series of units, each including a diaphragm and a cooperating resonator: the diaphragm and resonator, or at least the lat-- ter. being tuned to one of the notes of the musical scale.

It is within the scope of my invention to provide one such unit for each note of the useful audible scale; and when so arranged the response of each unit to its own fundal a mental and the harmonic overtones therei so vigorous that it predominates over all o....er W123. This results in a faithful reproduction of the composite tone. In the case large instruments, designed for auditotheaters and the like, such a constructi be found very efiicient; but as prope1. gned diaphragins and rcsonatorstor tl octaves involve large dimensions, ich a con ruction would probably be im- Jactical mr instruments; of moderate size. I have found that verytistactory-results can be obtained with as 1.1er instrun'ient containing twelve units -one for each note 0' the chromatic scale. Since such units, howevtr, will not re id satisfactorily to notes lower than their iun-damentals. it would theoretically be desirable to utilize the lowest des ablcoctave. Such an instrument, however, would be impractical for many purposes, in view of the large dimensions received to produce resonance to notes of the low octaves. It is, therefore. preterable to select twelve units corresponding to the notes of one of the lower middleoctaves. These will respond accurately to all oscillations corresponding to their fundamentals and to all the overtones, which, of course. includes the higher octaves. In such case, however, it will be necessary to provide other means for producing the notes of lower register, and .one such means consists in the association, with twelve such tuned units, of

' ting or sounding body primarilyreve only to such lower notes. Especially is this etlective it means are also provided to minimize actuation 01 this body at the higher frequencies.

One such means herein illustrated and hereinat'ter described in this specification. and consists, generally, in providing a diaphragm, cone or sounding-board of relatively large dimensionsuiiiciently large and of such character and mounting as to possess a negligible natural or fundamental frequency. If this sounding body is actuated by an electromagnetic unit provided with means for filtering out the higher frequencies, it will respond with substantial accuracy to such lower notes, while the tuned units will simultaneously respond to the upper partials of these notes: and thus there will be produced music particularly beautiful and agreeable.

Still another feature of my invention is important. It is a characteristic of resonating chambers, employed as sound amplifiers, that a certain amount of energy in-put is required to bring them .into full resonance; and it is only in this condition that such chambers are completely selec-live. On the other hand, if the energy is increased beyond this point, the sound becomes unpleasant. As exquisite expression, with corresponding enjoyment, can only be attained by varying the total volume of sound projected from the instrument. It is an object of this invention to provide means whereby the sound resonators can be operated at or near full resonance, while the total volume of sound, projected into the room or auditorium, can be modulated at the will of the operator. One such means is herein disclosed and consists in placing the sound producers in a cabinet as sound-proof as practicable, and providing means, such as shutters or other outlet controlling means, to vary the volume of sound permitted to escape.

Other features of my invention willappear hereafter in the specification.

Referring, now, to the accompanying drawings, illustrating one embodiment of my invention,-

Figure 1 is a cross section of a loud speaker involving my invention.

Figure 2 is a cross section at right angles to Fig. 1.

Figure 3 is a vertical section of a modification.

Figure 4 is a vertical section of the same modification, at right angles to Fig. 3.

Figure 5 is a top plan view of the same form, with cover removed and louvers open.

Figure 6 is a section along the lines 6-6 of Fig. 2.

Figure 7 is a sectional view of a modification.

Figure 8 is a diagram showing how the. various parts are connected together.

Similar numerals indicate like parts in all the drawings.

I have chosen, for illustration, a compact form of my invention, designed for private use. in which the number of units has been limited to twelve, in accordance with the. principles hereinbetore' discussed. As illustrated in Figures 1 and 2, and with some modification also in Figures 3 to 7, therefore,

the numeral 33 designates a cabinet which is, preferably, substantially sound proof. The twelve units may be arranged with the horns vertical and their mouths substantially in the same plane. They are preferably arranged in three rows of four each, as will be seen in Fig. 3. With the horns arranged in this manner, the longest resonator which it is practical to place in such a cabinet, will respond,substantially, to a note of C2. The other eleven units will then rise in pitch, progressively, by semi-tones. This arrangement makes it necessary, for faithful reproduction, separately to produce and amplify the low notes. The horn and operative units therefor may be of any desired type which may be separable for applying such devices as are de scribed in my co-pending application which has been formed by division from the present application.

It is desirable, for many purposes, that the entire volume of sound be under the control of a single instrumentality. 1, therefore, prefer to install a low frequency reproducer within the cabinet. There is, therefore, provided within the cabinet, a large resounding member, soundingboard or diaphragm, 341-, which may be supported by brackets attached to the side walls of the cabinet. These brackets are adapted to have the ends of the diaphragm extend between them, and to be clamped by them. It is preferable, however, that a resilient washer 35 be interposed between each of the brackets and the dia:

phragm, in order toinsure that rattling shall not occur; and for this purpose washers, made of cork, in the condition previouslv described, that is, previously compressed to less than one-half of its original thickness, are eminently satisfactory.

The brackets may conveniently be in the form of angle irons, having one of the angle faces resting upon the cork washers, and having the other attached to the inside of the casing. I prefer that the angle irons, cork washers and diaphragm, shall be rigidly attached together, as by bolts 37, extending through the parts.

The numeral 38 designates an operating unit of any efficient type, responsive to the low registers and having a projecting pin 39 extending upwardly toward, and in engage ment with, the diaphragm. For many purposes, it may be desirable to attach the said pin 39 to the diaphragm, but I have produced satisfactory results by bringing the pin into pressure contact, only, with the diaphragm. WVhere such a form is used, the construction of the units should be such as to create, within the unit, a bias outwardly suflicient to cause the pin and diaphragm to be in such contact as is desired, while the armature of the speaker unit is in the center of its path of travel. In this manner the pressure creates a tension, in the diaphragm, which improves its action. I make'no claimto this feature, however, in this application, asthe same forms the subject .matter of another application about to be filed by me. The loud speaker unit may be supported from the bottom by suitable brackets 40.

The various reproducing units described are preferably electrically connected in such manner asto permit the low frequency waves selectively to. operate the aperiodic speaker and to permit thehigh frequency waves selectively to operate the sympathetic resonant units. A practical manner ofacconn plishing this is to connect the three units of each column in series, and to connect the four columns in multiple. This set, so connected, is then placed unit.

In order to facilitate the passage of the high frequency notes (and by this term I am indicating generally notes higher than the lowest not of the tuned units), the-operating coil 41 of the aperiodic unit 38 has, in shunt with it, a condenser 43, and it will be understood that the coil 41 and condenser 43 will be so chosen, relative to each other and relative to the impedance of the high frequency circuit, as to bypass thehigh frequency currents around the coil 41.

A variable resistance 44 is also preferably placed in shunt with the coil 41, in order to vary the volume of sound coming from the aperiodic speaker, and to vary the relative proportion of the sound produced by the aperiodic speaker and by the resonant units. This resistance should have a minimum value materially less than the impedance of the coil 41, and should have a maximum so much higher than the coil 4-1 that it is without sub stantial effect.

The control of the volume of the sound, as

in series with the aperiodic accomplish this result, the sound proof casmg is preferably provided with a lid or cover 45, hinged at the back, as shown at 45 and arranged to be raised, lowered and held in either position. With such a lid raised to an angle of 45 degrees, the sound waves, issuing upwardly from the horns and diaphragm will be deflecteddirectly, outwardly, toward the audience. A change in the angle of the lid, however, will correspondingly change the direction of the deflected tone, so that it may be caused to produce different effects.

In the upper half of the cabinet, between the horns and the deflector, are placed a series of louvres 46, which are pivoted upon the axes 41:? carried by the side walls of the frame, said louvres being so spaced, relative to each other that when in horizontal position, they cut of, substantially, all of the emission of sound. lVhen, however, they are slightly displaced from the horizontal position, a passageway is formed for the emission of sound, but in this condition the louvres are at such an angle that the sound is deflected, by them, before reaching the cover 45. It thus has its normal course changed and is not reflected toward the audience. The effect is thus softened and changed. As illustrated, the louvres are arranged to be moved in unison by a rod 49, which may be connected to each of them by a ball and socket joint 50. The rod 49 projects outwardly of the machine to an operating handle 51 and operates in a slot 52 in the casing.

The louvres are designed to make a substantially tight closure when in the closed position, and to this end there may be provided, within the cabinet, projections 53 and 54- on opposite sides of the cabinet, in position to engage one edge of the end louvres; and each of the louvres may be provided with a felt strip 55, in position to engage the next louvre when the louvres are closed.

It is desirable that the louvres shall operate noiselessly and without lost motion, that they shall offer little obstruction to the passage of sound, in the open position, and that they shall effect as complete a suppression of all sound, when in the closed position, as is possible. These results are, in part, accomplished by the provision of the ball and socketjoints above referred to, and of the felt strips; but it is also desirable that the louvres, themselves, shall be made of a nonresonant material such, for example as an alloy of lead.

It is desirable, for the production of certain musical effects, that the relative operation of the low tone reproducer and of the resonant reproducers be alterable from the outside. The resistance 44 may, therefore, conveniently be made in the form of a small rheostat 57, operated by a control handle 58 extending out of the cabinet. Vith the above construction it will be obvious that the sounds, issuing from the horns and from the diaphragm 33, will be blended within the cabinet and the horns may be kept in full resonance at all times, since the volume of sound is controlled by the louvres. Should it be desired, however, to strengthen the bass or the treble, this may readily be done by the control handle 58.

In the modification, illustrated in Figs. 3, 4, 5, and 6, the aperiodic element is in the form of a large diaphragm 60, which is placed opposite to, and substantially close. a corresponding opening (31, in one of the side walls of the casing. This diaphragm maybe held in place between cork washers by screws 63 so that, to outward appearance, the diaphragm forms a panel in the wall of the casing. The operating unit 65 may be supported by a bracket 66, extending from one side of the casing to the other and held to the side walls by screws 67.

lVith this modification of the device, the louvres do not materially affect the volume of sound issuing from the aperiodic diaphragm, since the greater portion of this sound is communicated directly to the external air. There is, therefore, also provided a rheostat 70, under control of a handle 71, which is in shunt with the operating unit 38, as in the previous modification. It will be observed, however, that the function of the rheostat, in this instance, is to assist in control of the volume of sound by controlling the volume of the bass. The proper control of sound volume may now be obtained from the treble notes, through the louvres, and from the bass notes, from the rheostat. Thus, the co-joined use of these two instrumentalities can produce any volume of sound desired, and any relative proportion between treble and bass. Suitable binding posts 73 and 74., may be provided for introducing the electric energy into the magnet.

In the form of the invention illustrated in Fig. T, there is a slight inodilicatimi of the device, in that the cabinet 80. in which the horns are placed. encloses only the months 81. r

of the horns. This is su'tlicient to effect a substantial blending of the music produced by the horns, and to enable the volume satisfactorily to be controlled, since the volume of sound issuing from the mouths of the horns is far greater than that which radiates from the metal of the body of the horn.

This form of cabinet may be provided with the same type of louvres and deflector cover which has previously been described.

By the above construction it will be clear that those higher tones and overtones, on the faithful reproduction of which so much of the beauty of music depends, are separately produced in pure form and resonantly ainplified, while the entire construction of the apparatus serves to accentuate the true harmonic tones and overtones, with a virtual suppression of all inimical vibrations.

As I have already pointed out, the forms of apparatus embodying the various features of my invention, shown in the accompanying drawings or described in the specification, are merely illustrative of one or more ways in which the invention may be carried out.

eluding a resonant chamber, said units being tuned to separate fundamental notes, and means for suppressing at least some of the sound from all of said units simultaneously independent of the actuation thereof.

2. In an acoustic device in combination, a plurality of sound producing units each in cluding a resonant chamber tuned to a particular note of the chromatic scale, means for confining the sound issuing from said units, including means for controlling the sound issuing from said confinement.

3. In an acoustic device in combination a plurality of sound producing devices, each fundamentally responsive to one of the diatonic notes of the scale, a reson ating appara- I tus associated With each of said devices, responsive to the same fundaniental, and com mon means for operating all of said devices.

4. In an acoustic device in combination means for producing notes of higher frequency and means for producing notes of lower frequency, and means for lay-passing the high frequency energy about the low frequency producer.

5. In an acoustic device in combination a means for producing and. resonantly amplifying notes of high frequency, and separate means for producing in ample vol une notes of loW frequency.

6. In an acoustic device in combination aperiodic means for reproducing and amplifying the lower notes of theregister, and means including a plurality of dilferently tuned elements for reproducing and amplifying the higher notes of the register.

7. In an acoustic device in combination aperiodic means for reproducing and amplifying the lower notes of the register, and a plurality of tuned reproducing elements, each adapted to reproduce and amplify a selective group of tones and combinedly designed to cover the entire musical range not covered by said aperiodic means.

8. In an acoustic device in combination a plurality of sound producing units tuned to different notes of the chromatic scale, an aperiodic sound producing unit tuned to lower notes and means for mingling the sound produced from said different units, and means for controlling the volume of sound Without affecting the resonance.

9. In an acoustic device in combination means for producing a plurality of sounds in the upper portion of the audible range, means for separately resonantly amplifying each of said sounds and separate means for producing and amplifying sounds of loW register. I

10. In an acoustic device in combination a soundproof chamber, an aperiodic reproducer particularly responsive to bassnotes and a reproducer including resonant amplifiers both of said reproducers being housed within said chamber and common means for controlling the issuance of sound produced by .both of said reproducers from said cham her. I I

11. In an acoustic device in combination a soundproof chamber, an aperiodic reproducer particularly responsive to bass notes and a reproducer including resonant amplifiers both of said producers beinghoused Within said chamber, common means for controlling the issuance of sound produced by both of said reproducers from said chamber, and independent means for varying the proportions of the sound of the one instrument relative to the other.

12. Means for producing compressional Waves, comprising in combination a plurality of open ended casings forming resonators tuned to different predetermined Wave frequencies' respectively, an aperiodic reproducer, and means responsive to oscillatory energy of complex Wave form for causing actuation of said resonators selectively in response to predetermined components of the energy, and for actuating the aperiodic re producer in response to other components of the energy.

13. Means for reproducing energy compressional Waves, comprising a plurality of Waves comprising in combination, a plurality of variously characterized open ended casings each defining a column of compressible medium resonant to a relatively difi'erent predetermined Wave frequency a plurality of vibratory elements, at least one for each of said casings, forselectively resonating the medium Within the casings, an aperiodic reproducer for producing Waves of frequency below the frequency range of said resonators, and means for impressing oscillatory energy of complex Wave form upon said elements and reproducer.

16. Means for producing compressional Waves of complex Wave form, comprising 1n combination, actuating elements, and resonating chambers controlled thereby and defining unequal volumes of compressible medium so as to resonate to relatively different components of Waves produced by the actuating elements.

17. The method of producing compres- ('3 gamma s'io'nal waves, which includes the step of 'empImsizin-g a predetermined component of the sound Waves by resonatmg a restncted n Volume 'of a natural medium.

Signed at New York, in the County of New York and State of New York, this third day of January A. D. 1927.

MILLER REESE HUTCHISON. 

